The genus Trachyopella Duda, 1918 is revised to include 19 species in the Holarctic Region (4 Nearctic, 8 Palaearctic, 5 Holarctic, 2 cosmopolitan). Ten new species are described, viz., T. operta sp.n. (N. Korea), T. hem sp.n. (Azores, Madeira, Canary Is.), T. nuda sp.n. (Canada, USA, Bermuda), T. binuda sp.n. (USA: Florida), T. artivena sp.n. (N. Korea), T. pannosa sp.n. (Yemen), T. mitis sp.n. (N. Korea), T. senaria sp.n. (USA: Florida), T. pectamera sp.n. (USA) and T. straminea sp.n. (Holarctic). The genus is divided using cladistic methods into 4 subgenera, viz., Nudopella subg. n. (type species: Limosina leucoptera Haliday), Insulomyia Papp, 1972 stat.n. (type species: Insulomyia microps Papp), Minuscula subg. n. (type species: Trachyopella minuscula Collin) and Trachyopella s. str. (type species: Limosina melania Haliday).
New diagnoses are given of the genus Trachyopella and its subgenera and all species under study are described, keyed and illustrated in detail. Biological and distributional data are summarized for each species. Type material of all known Holarctic species was examined and 6 lectotypes are designated. Trachyopella ealensis Vanschuytbroeck, 1951 is synonymized with Spelobia bifrons (Stenhammar, 1854). An attempt is made to display supposed interrelationships within the genus on the basis of cladistic principles and the zoogeography of the genus is discussed.